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njit-etd2003-081 - New Jersey Institute of Technology

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11<br />

mechanism behind HRV in both normal and COPD. The ARX model for each subject<br />

consists <strong>of</strong> filtered inputs plus additive noise and the output is the heart rate variability<br />

signal under investigation. Non-parametric relationships between the inputs (respiration<br />

and BP signals) and output (HRV) <strong>of</strong> the model will result in transfer function<br />

estimation <strong>of</strong> the noise filters and the input filters <strong>of</strong> these highly non-linear models.<br />

Through a series <strong>of</strong> model transformations, the cardiovascular control<br />

mechanism can be expressed as a multiple-input single output linear system. The<br />

estimation <strong>of</strong> parameters for this class <strong>of</strong> ARX models is then defined as a maximum<br />

likelihood estimation (MLE) problem through state-space representations <strong>of</strong> input filters<br />

and noise filters. MLE techniques available in the MatLab System Identification<br />

toolbox then provide the means by which these ARX models can be parameterized to<br />

describe the observed HRV.<br />

5. A severity-classification technique <strong>of</strong> the COPD disease states is developed using<br />

principal component analysis and cluster analysis on HRV parameters to identify and<br />

classify different subjects into proper disease states. In COPD, this helps identify severe<br />

patients who may be best candidates for surgery while in other diseases it may provide<br />

more accuracy and information in diagnosing a particular disease.

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